184 MORPHOLOGY AND EVOLUTION
variable number of ribs (Orang, 1 to 10; Gibbon and Chimpanzee, 1 to 11; Gorilla, 1 to 13). It has a thick insertion into the whole length of the vertebral border of the scapula. Its nerve supply is great in the Chimpanzee.
The eoraeo-bracMalis arises from the tip of the coracoid process along with the short head of the biceps. Wood (164) showed that it is really a triple muscle, consisting of long, middle and short parts. The short part, running to the shaft of the humerus above the teres major, is absent in the Apes. The middle part, running to the middle of the shaft of the humerus, is present in all Apes. And the long part, which runs to the internal intermuscular septum and dorso-epitroch-learis is only present in the Orang and Chimpanzee ; the musculo-cutaneous nerve passes between the parts. In Man the long and middle parts are fused, and the nerve perforates the muscle.
The biceps flexor cubiti* is similar in Man and the large Apes, but the two heads unite higher up in Man. In the Gibbon the long head is as in Man, the short head arises from the bicipital groove; and fibres spring from the entire length of the internal intermuscular septum, thus concealing the brachial vessels and nerves. The lacertus fibrosus is reduced in the Apes. In some cases the biceps in Man is as in the Gibbon.
The brachialis anticus is built on the same plan in the Apes and Man. Hepburn (83) states that it does not embrace the insertion of the deltoid, but I found it doing so in a Chimpanzee. The coraco-brachialis, biceps and brachialis anticus are supplied by the musculo-cutaneous nerve.